Validation Study on Jason-2 Rain Flag and Rain Rate Estimation Over North Indian Ocean

This letter reports the results of the validation study on Jason-2 (JA2) rain flag and rain rate (RR) estimation over North Indian Ocean for the first time. This study was performed using 12 months of Geophysical Data Record (GDR) and collocated Microwave Imager and Precipitation Radar (PR) observations onboard Tropical Rainfall Measuring Mission (TRMM) employing strict spatial and temporal collocation criteria. The present study brought out that rain flag parameter available in GDR was not triggered during rain events, and an attempt is made to recompute the same using a novel method of differential attenuation between Ku band and C band backscatter. The score of rain detection using recomputed Ku/C mean rain-free relation is found to be about 98%. The high rain detection by JA2 clearly demonstrates the performance of the dual-frequency rain flagging while considering the high temporal and spatial variability of the rain. The comparison of RR estimated from JA2 with TRMM sensors was in good agreement. The results of the present study thus accentuate the need for better rain flagging over regional oceans which is essential to evade erroneous values in altimetric geophysical parameters.